The changes in chemical composition and physical properties that accompany bio-oil aging reactions have been studied earlier. However, one fundamental aspect of this transformation process has been ignored. In this article, we prove that aging of fast-pyrolysis bio-oils from woody biomass is an exothermic process with notable heat generation under adiabatic conditions. The heat generation characteristics of several fast-pyrolysis bio-oils were studied in a novel reaction calorimeter that was made in-house. When typical fast-pyrolysis bio-oils were stored at 50 °C for a period of 1 week, they exhibited overall adiabatic temperature increases ranging from 14 K to 28 K. The largest differences in heat generation were observed at the beginning of the aging period, which corresponds with the previously known reactivity characteristics of bio-oils. Increasing the storage temperature accelerated the aging reactions, which manifested as higher overall temperature increases-up to 55 K in 1 week-and higher specific thermal power density (STPD) values. The reactivity of the bio-oil at 70 °C could be partly passivated by employing a 1 week pretreatment at a more moderate temperature (40 °C). The addition of alcohol decreased heat generation from the bio-oil. The observed heat generation of bio-oils under varying aging conditions correlated with changes in their chemical composition and physical properties. This shows that previously developed bio-oil stability indicators can also be used to estimate the heat generation potential of a given bio-oil. In particular, a change in the concentration of carbonyl compounds exhibited a clearly linear correlation with heat generation. A decrease of one unit in the carbonyl content (mol/kg of bio-oil) would correspond to an adiabatic temperature increase of 20 °C.
- heat generation
- pyrolysis bio-oil
Sundqvist, T., Solantausta, Y., Oasmaa, A., Kokko, L., & Paasikallio, V. (2016). Heat generation during the aging of wood-derived fast-pyrolysis bio-oils. Energy & Fuels, 30(1), 465-472. https://doi.org/10.1021/acs.energyfuels.5b02544